Spring forming machines, also known as spring coilers, comprise a device for forming spiral springs comprising supplying rolls advancing a wire, normally of metal, through a guide, to coiling tools provided with coiling tips provided with a wire guide. The coiling tips are placed so that, as the wire is gradually supplied, these can deform the wire so that this latter takes a cylindrical shape having a diameter corresponding to the spring diameter, while a further tool makes a determined pitch, so that the spring takes the turn shape typical of the compression springs. When the so formed spring has reached the desired length and number of turns, a cutting tool separates the spring from the unwound wire, so that it can be worked with the said steps for forming another spring.
The springs must be manufactured with a predefined pitch, number of turns and length, falling into determined tolerance limits.
Moreover, the machine comprises a vision system performing a scan of the formed spring, which is delivered to a control unit of the machine itself for verifying the spring dimensional parameters.
Downstream the forming device, the machine further comprises a selecting device which, based on the result of the step of verifying the parameters performed by the control unit, subdivides each formed spring in two or more groups, for example subdivides the springs in a first group corresponding to springs falling into the predefined tolerances, and in a second group comprising out-of-tolerance springs. As an alternative, the selecting device can subdivide the manufactured springs in more than two groups. Generally, the selecting device comprises an inlet in which the springs formed into the forming device enter, and at last two distinct outlets subdividing the springs into distinct groups according to what has been discussed before. One or more movable blades, commanded by the control unit, guide the entering spring towards the outlet corresponding to the group to which the spring is destined.
More and more stringent tolerances, with higher and higher manufacturing speeds, determine an increase of the rate of errors during the selection because of the present selecting technology. Therefore, an out-of-tolerance spring can by mistake fall in the group of the suitable-deemed springs. Therefore, a run of suitable-deemed springs could on the contrary comprise one or more out-of-tolerance springs, so that this run will be entirely compromised for this reason.
A further problem that can happen is caused by a spring jammed inside the selecting device, which can be consequently damaged and then conveyed to the suitable spring group.
Even though the dimensional analysis and the following step of subdividing the springs into groups are correct, what was discussed hereinbefore happens substantially due to a less than perfect synchronization between the springs dropping into the selecting device and the real selection made by the selecting device.
For solving this lack of synchronization, the operator must act on the set operative parameters of the selecting device, which particularly comprise a delay (in other words the time between the instant in which a finished spring is in the dimensional analysis area and the instant in which the spring enters the selecting device) and the effective duration of the selection (in other words the time between the instant in which the spring enters the selecting device and the instant in which exits the same).
At each spring forming cycle performed by the new set parameters of the selecting device, it is necessary to check again the correct subdivision of the spring into the predefined groups, which, due to the stringent tolerances, is complicated and burdensome since it is generally required the use of accurate measuring instruments, typically located in rooms different from the ones in which the coiling machine is placed. In any case, such checks do not ensure the set parameters of the selecting device are correct and perfectly centered in order to avoid the generation of further selection errors.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.